1. Field of the Invention
The invention relates to an adjusting element having a cylinder, the interior space of which contains a pressurized medium, having a piston which is arranged displaceably in the cylinder and has a piston rod which protrudes out of the cylinder at one end of the cylinder, having an annular seal which surrounds the piston rod and, with its inner, radially encircling circumference, bears in a sealing manner against the piston rod and, with its outer, radially encircling circumference, bears in a sealing manner against the inner wall of the cylinder, is acted upon, on its side facing the interior space, by the pressure of the medium and, with its side facing away from the interior space, is supported on a supporting element, which, in turn, with its end facing away from the annular seal, is supported on part of the cylinder, it being possible for the supporting element, when a certain bearing force of the annular seal against the supporting element is exceeded, to be deformed somewhat telescopically, reducing its axial length in the cylinder, from a normal position into an overload position, as a result of which a passage opening from the interior space of the cylinder to the surroundings can be produced.
2. Description of the Prior Art
In the case of adjusting elements of this type, which are preferably gas-filled springs, the interior space, which is filled with the medium, can be connected to the surroundings when a certain internal pressure of the cylinder is exceeded, in order to avoid excessive internal pressure in the cylinder. An excessive internal pressure, which can arise due to an increase in temperature, for example in the event of burning in the vicinity of the adjusting element, or else also due to deformation, may result in the cylinder being destroyed or in the piston rod being pushed out of the cylinder.
Gas-filled springs of this type may, for example, be pneumatic adjusting elements for ease of operation of the trunk lid or the engine hood of a motor vehicle, said adjusting elements forming a weight counterbalance to the parts which have been adjusted.
An adjusting element of the type mentioned at the beginning is disclosed in DE 41 01 567. When the defined bearing force of the annular seal against the supporting element is exceeded, the annular seal is displaced toward the opening from which the piston rod emerges from the cylinder and thus opens up a hole in the cylinder, via which the interior space of the cylinder is connected to the surrounds thus enabling the medium contained in the cylinder to escape into the surroundings. In this case, it is disadvantageous that moisture can enter into the cylinder through the hole, which results in corrosion.
A further known adjusting element (DE 24 57 938 C2) has a predetermined breaking point which breaks when overstressed thus enabling the gas contained in the interior space of the cylinder to escape to the outside. This predetermined breaking point can be formed on the cylinder wall or on the piston rod, which is provided with an outwardly closed coaxial hole. When a certain bursting pressure of the cylinder is exceeded, the parts separated at the predetermined breaking point can fly around and cause damage.
DE 195 35 711 C1 discloses an adjusting element which has, for the piston, a stop which is designed as a sleeve and which limits the outward movement of the piston and piston rod. The sleeve consists of a material which can melt above a defined temperature. If the temperature increases beyond the defined temperature, then the sleeve melts and the piston can be displaced further outward. In the process, a bypass to the outside is provided, the bypass circumventing the annular seal and enabling the gas contained in the cylinder to escape. This bypass is formed by a cross-sectional tapering of the piston rod, but results in the piston rod being weakened.